No, the superlative degree is "most tirelessly."
the superlative degree of much is most
The superlative degree of stout is stoutest.
The superlative degree of "broad" is "broadest."
"Fool" is a verb and a noun and, as such, does not have a superlative degree. The superlative degree of the adjective foolish is most foolish.
"Less" is the comparative degree of little. The superlative degree is least.
Thinnest is the superlative degree of thin.
most often is the superlative degree for often
No, the word tirelessly is an adverb, which modifies a verb as done without yielding to fatigue; continuing, persistent. The noun form is tirelessness.John worked tirelessly to obtain his degree.
Cleanest is the superlative degree of the word clean. Cleaner is the comparative degree
The superlative degree of "splendid" is "most splendid."
The comparative degree of cheerful is more cheerful.Its superlative degree, then, is most cheerful.
positive degree=few comparative degree=fewer superlative degree=fewest